Not applicable.
The present invention relates to a method and an apparatus for delivering a liquefied compressed gas from a tube trailer or other supply source to a use point, such as a semiconductor fabrication tool or facility, and in particular to a method and an apparatus for detecting the occurrence of a liquid dry condition.
Reference is made to use of the invention for detection of an occurrence of a liquid dry condition in high-pressure tubes of hydrogen chloride (HCl). (The tubes are elongated cylinders which are stacked one upon the other on a trailer for transportation of chemicals and gases, as is well known in the industrial gas industry.) However, the invention can be used in connection with other types of liquefied compressed gases and other types of containers.
High-purity HCl is used for certain semiconductor processes, such as silicon epitaxial deposition. Bulk HCl is delivered to semiconductor customers in tube trailers, which include multiple tubes typically rated to 1800 psig. At 70xc2x0 F., HCl exists as a compressed liquefied gas under its own vapor pressure of 629 psig. Customers draw the vapor from each tube to feed their specific process applications, such that one tube serves as the source of gas until it is considered to be empty, when a crossover panel then changes (or crosses over) the source to the next available tube of gas.
It is desirable to determine when each HCl tube is near xe2x80x9cemptyxe2x80x9d for several reasons. The customer desires to use as much HCl from each tube as possible, since they are billed per full trailer of product delivered, not by the amount of product that is used. It is undesirable, however, to draw product from tubes that are sufficiently empty that the product exists only in a gaseous phase, commonly referred to as a liquid dry condition. The liquid dry condition causes an increase in the levels of impurities of lower volatility in the gas stream, including an increase in moisture level, which causes corrosion. This could result in lower semiconductor yields.
A liquid dry point occurs when a pressurized liquefied compressed gas, such as HCl, in a container (such as a tube) is slowly vaporized for saturated gaseous supply, as follows. When substantial amounts of the HCl exist in the liquid phase, the pressure of the system remains relatively stable during the release and delivery of the saturated gaseous HCl because the liquid portion vaporizes with the input of heat from the environment. Eventually a physical state occurs where all of the liquid has been vaporized and the remaining HCl exists in an entirely unsaturated, gaseous phase. At precisely this moment, a liquid dry condition has occurred, wherein the pressure of the container decays rapidly thereafter.
Moisture and volatile metallic compounds can typically increase significantly after the liquid dry point is reached in liquefied compressed gas such as HCl. When a two phase system exists in a container (such as tube trailer), a vapor liquid equilibrium is maintained. Contaminants such as moisture and volatile metals have very low partition coefficient and concentrate more in the liquid phase leaving the vapor phase much cleaner. (Partition coefficient is the ratio of the concentration of a volatile component in the gaseous phase to its concentration in the liquid phase when the system is in vapor liquid equilibrium.) These contaminants get more concentrated as HCl preferentially vaporizes as ultra-pure product during transfer and delivery to the use point. Upon reaching the liquid dry point, due to the absence of the liquid phase, moisture and volatile metals are free to pass with the delivered gas. Therefore, when liquid dry point is reached, higher than normal levels of moisture or any volatile metals are experienced in the delivery of final gaseous product from the source of supply (such as tube trailers). It is therefore desirable to detect the approach or obtaining the liquid dry condition.
Devices such as mass flow meters or mass flow totalizers have been unreliable in HCl service and therefore cannot be used to detect liquid dry conditions based on mass balance calculations. Typically, a weigh scale is used to identify when a tube is approaching a liquid dry condition. However, this usually requires leaving a nominal liquid heel in the tube, making it less than an optimal solution. Also, the purchase and installation of a scale requires a large capital investment.
An alternate method of identifying when a tube is approaching a liquid dry condition is disclosed in U.S. Pat. No. 5,359,787 (Mostowy, et al.). Sensors, such as thermocouples and pressure transducers, are provided for the source supply (e.g., a tube trailer) and the ambient temperature conditions. The ambient temperature at the source supply is sensed, the temperature of the chemical from the source supply is sensed, and the relative change in pressure over selected time intervals is sensed and transmitted to a digital computational controller. These values are compared against preset values for ambient temperature, source of supply temperature and pressure indicative of the liquid dry point (gas phase), and when the sensed values exceed the prescribed preset values which indicate the liquid dry point is reached, the controller provides an appropriate alarm signal.
U.S. Pat. No. 5,359,787 teaches that the liquid dry point also can be calculated by determining and inputting to the digital computational controller the volume of the tube trailer, the weight of the trailer during transfer of the liquefied compressed gas, and the ambient temperature at the tube trailer, as well as the temperature of the chemical leaving the tube trailer and entering the delivery conduit. These values are compared to preset values already input into the controller which represent approach to substantially gas phase of the chemical (meaning that at least some small amount of chemical is still in the liquid phase). When the sensed values meet or exceed the preset values so as to indicate the approach to the liquid dry point (substantially a gas phase), the system generates an alarm signal.
Neither of the methods disclosed in U.S. Pat. No. 5,359,787 for identifying or determining the liquid dry point works as well as the present invention, which provides a more exact method for detecting the occurrence of a liquid dry condition using a more quantitative approach.
It is desired to have a more cost effective, reliable method of detecting the occurrence of a liquid dry condition in a container of liquefied compressed gas, such as HCl.
It is further desired to have a more cost effective, reliable method of delivering a high-purity industrial chemical in gaseous phase from a transport vehicle having multiple tubes which contain the chemical in a liquefied compressed gas phase. It also is desired to have an improved transport vehicle for delivering a high-purity industrial chemical in gas phase.
It is still further desired to direct the changing (or crossover) of tubes in a tube trailer or other bulk delivery system in an optimal manner.
The present invention is a method and an apparatus for detecting an occurrence of a liquid dry condition in a container containing liquefied compressed gas. The present invention also includes a method and an apparatus for directing a crossover to a second supply of liquefied compressed gas upon the occurrence of a liquid dry condition in the container. In addition, the present invention includes an improvement to a transport vehicle (e.g., a tube trailer) for delivering a high-purity industrial liquefied compressed gas in gaseous phase and a method of delivering the high-purity industrial chemical in gaseous phase from the transport vehicle.
In a first embodiment, the method of detecting an occurrence of a liquid dry condition in a container containing a liquefied compressed gas while the gaseous phase of the liquefied compressed gas is being removed from the container over time comprises multiple steps. The first step is to measure the pressure (P) inside the container over time. The next step is to measure the temperature (T) inside the container over time. The third step is to determine a rate of change in the pressure (dP/dt) inside the container over time. The next step is to determine a rate of change in the temperature (dT/dt) inside the container over time. The final step is to identify an occurrence of a sudden increase in the rate of change in the temperature (dT/dt) inside the container and a substantially simultaneous occurrence of a sudden decrease in the rate of change in the pressure (dP/dt) inside the container, said substantially simultaneous occurrences indicating an occurrence of a liquid dry condition in the container.
In a second embodiment, the method of detecting the occurrence of a liquid dry condition includes two additional steps. The first additional step is to monitor the ambient temperature (Ta). The second additional step is to account for a change in the ambient temperature in determining the rate of change in the temperature (dT/dt) inside the container over time.
A third embodiment of the invention is an apparatus for detecting an occurrence of a liquid dry condition in a container (22 or 24) containing a liquefied compressed gas while the gaseous phase of the liquefied compressed gas is being removed from the container over time. The apparatus includes a first sensor (12), a second sensor (14) and a computer (16). The first sensor senses temperature (T) inside the container and provides a signal indicative thereof. The second sensor senses pressure (P) inside the container and provides a signal indicative thereof. The computer receives signals from the first and second sensors, and determines rates of change in the pressure (dP/dt) and the temperature (dT/dt) inside the container over time. The computer also identifies an occurrence of a sudden increase in the rate of change in the temperature (dT/dt) inside the container and a substantially simultaneous occurrence of a sudden decrease in the rate of change in the pressure (dP/dt) inside the container, said substantially simultaneous occurrences indicating an occurrence of a liquid dry condition in the container.
In the preferred embodiment, the computer (16) is a programmed logic controller (PLC). The first sensor (12) preferably is a thermocouple, and the second sensor (14) preferably is a pressure transducer. The apparatus also may include an alarm (34) to report the occurrence of a liquid dry condition.
In a fourth embodiment, the apparatus also includes a third sensor (20) for sensing ambient temperature (Ta) and for providing a signal indicative thereof. The computer receives the signal from the third sensor and accounts for a change in the ambient temperature in determining the rate of change in the temperature (dT/dt) inside the container overtime.
In one variation of this embodiment, the computer accounts for a change in the ambient temperature (Ta) by a method comprising the following steps: (a) receiving the signals from the first and second sensors indicating the temperature (T) and the pressure (P) inside the container; (b) calculating a change in pressure inside the container over time xcex94Pt, a change in temperature inside the container over time xcex94Tt, and a change in ambient temperature over time xcex94Ta; (c) calculating       Δ    ⁢          xe2x80x83        ⁢          P      t            Δ    ⁢          xe2x80x83        ⁢          t      t      
and             Δ      ⁢              xe2x80x83            ⁢              T        t                    Δ      ⁢              xe2x80x83            ⁢              t        t              ,
wherein xcex94tt is an interval of time; (d) calculating             Δ      ⁢              xe2x80x83            ⁢              P        t                    Δ      ⁢              xe2x80x83            ⁢              T        t              ;
(e) comparing the value of       Δ    ⁢          xe2x80x83        ⁢          P      t            Δ    ⁢          xe2x80x83        ⁢          T      t      
with a first preset range of values referring to normal running conditions; (f) determining if the       Δ    ⁢          xe2x80x83        ⁢          P      t            Δ    ⁢          xe2x80x83        ⁢          T      t      
value is out of the first preset range of values; (g) if the       Δ    ⁢          xe2x80x83        ⁢          P      t            Δ    ⁢          xe2x80x83        ⁢          T      t      
value is out of the first preset range of values, calculating       Δ    ⁢          xe2x80x83        ⁢          T      t            Δ    ⁢          xe2x80x83        ⁢          T      a      
and             Δ      ⁢              xe2x80x83            ⁢              P        t                    Δ      ⁢              xe2x80x83            ⁢              T        a              ;
(h) comparing the calculated values of       Δ    ⁢          xe2x80x83        ⁢          T      t            Δ    ⁢          xe2x80x83        ⁢          T      a      
and       Δ    ⁢          xe2x80x83        ⁢          P      t            Δ    ⁢          xe2x80x83        ⁢          T      a      
with a second preset range of values for normal running conditions; (i) if the calculated values of       Δ    ⁢          xe2x80x83        ⁢          T      t            Δ    ⁢          xe2x80x83        ⁢          T      a      
and       Δ    ⁢          xe2x80x83        ⁢          P      t            Δ    ⁢          xe2x80x83        ⁢          T      a      
are out of the second-preset range of values, repeating steps (a) through (i).
In a fifth embodiment, the apparatus includes a data logging device for receiving the signals from the first and second sensor, and for converting the signals to the measurements of pressure (P) and temperature (T) inside the container at specific points in time. The data logging device also determines the rates of change in the pressure (dP/dT) and the temperature (dT/dt) inside the container over time, and records the measurements of pressure (P), temperature (T), and rates of change in the pressure (dP/dt) and the temperature (dT/dt) inside the container as a function of time. The data logging device also may receive a signal from the third sensor, convert that signal to a measurement of ambient temperature (Ta) at specific points in time, and record the ambient temperature (Ta) as a function of time.
A sixth embodiment of the invention is a method of directing a crossover to a second supply (24) of liquefied compressed gas upon an occurrence of a liquid dry condition in a container (22) containing a first supply of liquefied compressed gas while the gaseous phase of the first supply of the liquefied compressed gas is being received from the container over time. The method includes multiple steps. The first step is to measure the pressure (P) inside the container over time. The next step is to measure the temperature (T) inside the container over time. The third step is to determine a rate of change in the pressure (dP/dt) inside the container over time. The fourth step is to determine a rate of change in the temperature (dT/dt) inside the container over time. The fifth step is to identify an occurrence of a sudden increase in the rate of change in the temperature (dT/dt) inside the container and a substantially simultaneous occurrence of a sudden decrease in the rate of change in the pressure (dP/dt) inside the container, said substantially simultaneous occurrences indicating an occurrence of a liquid dry condition in the container. The final step is to actuate a crossover to the second supply of liquefied compressed gas upon identifying the occurrence of a sudden increase in the rate of change in the temperature (dT/dt) inside the container and a substantially simultaneous occurrence of a sudden decrease in the rate of change in the pressure (dP/dt) inside the container.
A seventh embodiment of the invention is a method of directing a crossover to the second supply of liquefied compressed gas which includes two additional steps. The first additional step is to monitor the ambient temperature (Ta). The second additional step is to account for a change in the ambient temperature in determining the rate of change in the temperature (dT/dt) inside the container over time.
In one variation of this embodiment, the second additional step (i.e., accounting for a change in the ambient temperature) comprises the following sub-steps:
(a) calculating a change in pressure inside the container over time xcex94Pt, a change in temperature inside the container over time xcex94Tt, and a change in ambient temperature over time xcex94Ta; (b) calculating       Δ    ⁢          xe2x80x83        ⁢          P      t            Δ    ⁢          xe2x80x83        ⁢          t      t      
and             Δ      ⁢              xe2x80x83            ⁢              T        t                    Δ      ⁢              xe2x80x83            ⁢              t        t              ,
wherein xcex94tt is an interval of time; (c) calculating             Δ      ⁢              xe2x80x83            ⁢              P        t                    Δ      ⁢              xe2x80x83            ⁢              T        t              ;
(d) comparing the value of       Δ    ⁢          xe2x80x83        ⁢          P      t            Δ    ⁢          xe2x80x83        ⁢          T      t      
with a first preset range of values referring to normal running conditions; (e) determining if the       Δ    ⁢          xe2x80x83        ⁢          P      t            Δ    ⁢          xe2x80x83        ⁢          T      t      
value is out of the first preset range of values; (f) if the       Δ    ⁢          xe2x80x83        ⁢          P      t            Δ    ⁢          xe2x80x83        ⁢          T      t      
value is out of the first preset range of values, calculating       Δ    ⁢          xe2x80x83        ⁢          T      t            Δ    ⁢          xe2x80x83        ⁢          T      a      
and             Δ      ⁢              xe2x80x83            ⁢              P        t                    Δ      ⁢              xe2x80x83            ⁢              T        a              ;
(g) comparing the calculated values of       Δ    ⁢          xe2x80x83        ⁢          T      t            Δ    ⁢          xe2x80x83        ⁢          T      a      
and       Δ    ⁢          xe2x80x83        ⁢          P      t            Δ    ⁢          xe2x80x83        ⁢          T      a      
with a second preset range of values for normal running conditions; (h) if the calculated values of       Δ    ⁢          xe2x80x83        ⁢          T      t            Δ    ⁢          xe2x80x83        ⁢          T      a      
and       Δ    ⁢          xe2x80x83        ⁢          P      t            Δ    ⁢          xe2x80x83        ⁢          T      a      
are out of the second preset range of values, repeating sub-steps (a) through (h).
An eighth embodiment is an apparatus for directing a crossover to a second supply of liquefied compressed gas upon an occurrence of a liquid dry condition in the container containing a first supply of liquefied compressed gas while the gaseous phase of the first supply of the liquefied compressed gas is being removed from the container over time. The apparatus includes the following: (1) means (14) for measuring the pressure (P) inside the container over time; (2) means (12) for measuring the temperature (T) inside the container over time; (3) means (16) for determining a rate of change in the pressure (dP/dt) inside the container over time; (4) means (16) for determining a rate of change in the temperature (dT/dt) inside the container over time; (5) means (16) for identifying an occurrence of a sudden increase in the rate of change in the temperature (dT/dt) inside the container and a substantially simultaneous occurrence of a sudden decrease in the rate of change in the pressure (dP/dt) inside the container, said substantially simultaneous occurrences indicating an occurrence of a liquid dry condition in the container; and (6) means (26, 28, 30 and 32) for actuating a crossover to the second supply of liquefied compressed gas upon identifying an occurrence of a sudden increase in the rate of change in the temperature (dT/dt) inside the container and a substantially simultaneous occurrence of a sudden decrease in the rate of change in the pressure (dP/dt) inside the container.
In a ninth embodiment, the apparatus for directing a crossover to a second supply of liquefied compressed gas upon an occurrence of a liquid dry condition in the container containing a first supply of liquefied compressed gas also includes: (1) means for monitoring the ambient temperature (Ta); and (2) means for accounting for a change in the ambient temperature (Ta) in determining the rate of change in the temperature (dT/dt) inside the container over time.
A tenth embodiment is a method of delivering a high-purity industrial liquefied compressed gas in gaseous phase from a transport vehicle having multiple tubes which contain the liquefied compressed gas in gaseous phase. The method includes multiple steps, as follows: (a) connecting a first tube (22) of the vehicle (18) to a delivery system (36); (b) discharging the liquefied compressed gas in gaseous phase over time through the delivery system; (C) detecting the occurrence of a liquid dry condition in the first tube (22); (d) automatically disconnecting (30) the first tube from the delivery system upon said detection of the liquid dry condition; (e) connecting (32) a next tube (24) of the vehicle to the delivery system; and (f) repeating steps (b) through (e) until the liquefied compressed gas has been discharged from all tubes of the vehicle.
In the preferred embodiment, the step of detecting the occurrence of liquid dry condition in the tube [i.e., step (c)] comprises multiple sub-steps. The first sub-step is to measure the pressure (P) inside the tube over time. The next sub-step is to measure the temperature (T) inside the tube over time. The third sub-step is to determine a rate of change in the pressure (dP/dt) inside the tube over time. The fourth sub-step is to determine a rate of change in the temperature (dT/dt) inside the tube over time. The final sub-step is to identify an occurrence of a sudden increase in the rate of change in the temperature (dT/dt) inside the tube and a substantially simultaneous occurrence of a sudden decrease in the rate of change in the pressure (dP/dt) inside the tube, said substantially simultaneous occurrences indicating an occurrence of a liquid dry condition in the tube.
An eleventh embodiment is an improvement to a transport vehicle (18) for delivering a high-purity industrial liquefied compressed gas in gaseous phase, the vehicle being of the type having multiple tubes (22, 24) which contain the liquefied compressed gas in gaseous phase. The improvement includes: (1) means (30) for connecting a first tube (22) of the vehicle (18) to a delivery system (36); (2) means (12, 14, 16) for discharging the liquefied compressed gas in gaseous phase over time through the delivery system; (3) means for detecting the occurrence of a liquid dry condition in the tube; (4) means (26) for automatically disconnecting the first tube (22) from the delivery system (36) upon said detection of the liquid dry condition; and (5) means (32) for connecting a next tube (24) of the vehicle (18) to the delivery system (36).